1. Field of the Invention
The present invention relates to a data communication technique used in a mobile communication network and, more particularly, to a method of processing an error frame that occurs in packet data communication between a mobile communication terminal and a communication server which exchanges packets with the mobile communication terminal over a radio network (RN).
2. Description of the Related Art
FIG. 1 is a block diagram showing a well-known 3GPP2 network topology. A mobile station (MS) 10 is indicative of a mobile communication terminal, such as a personal computer with wireless adapters, a mobile handset, a Wireless Application Protocol (WAP) terminal, or a mobile communication modem.
A radio network (RN) 20, also called a radio core network, is comprised of a base transceiver system (BTS) 21, a base station controller (BSC) 23, and a packet control function (PCF) 25. The RN 20 manages the mobility of the MS 10 and may authenticate the MS 10 using a Visitor Location Register (VLR) and a Home Location Register (HLR), which are connected to a mobile switching center (MSC) 30. The RN 20 controls data transmission between the MS 10 and a packet data serving node (PDSN) 40, and performs data buffering between the MS 10 and the PDSN 40. Furthermore, the RN 20 performs a paging process when data is transferred to the MS 10 over an Internet Protocol (IP) network.
Once a basic authentication process of a data call has been completed, a Generic Routing Encapsulation (GRE) protocol establishes a virtual connection between the RN 20 and the PDSN 40.
The BSC 23 provides call control and signaling function in addition to providing remote management function and hand-off function between BTSs and BSCs.
The BSC 23 communicates to the PDSN 40 through the PCF over the GRE tunnel. The PCF 25 and the PDSN 40 communicate with each other using a standard interface known as the RN-to-PDSN interface (R-P interface), which has two components: the A11 interface, used for control messages, and the A10 interface, used for user data. The PCF 25 provides data buffering and packet segmentation functions so that link layer packets received from the PDSN 40 can be transmitted to the MS 10 over an air interface. While the PCF 25 may be incorporated in the BSC 23, the PCF 25 is usually configured as a separate system.
The PDSN 40 provides access to the Internet, intranets, and WAP servers for the MSs that use the RN 20. The Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between the PDSN 40 and the MS 10. The PDSN 40 uses a Remote Authentication Dial-In User Service (RADIUS) server 50 for user authentication and traffic management, then forwards traffic to a gateway router/home agent at the designated IP network.
The RADIUS server 50 interacts with the PDSN 40 to perform AAA (Authentication, Authorization, Accounting) functions. That is, the RADIUS server 50 verifies that a user is a valid subscriber, determines what services are available for the user, and tracks usage for billing.
A Home Agent (HA) 60 maintains mobile user registrations and tunnels packets destined for the mobile client to the PDSN 40. The HA can perform dynamic home address assignment for the MS 10 from address pools configured locally, through Dynamic Host Configuration Protocol (DHCP), or from the RADIUS server 50. Upon receiving a registration request message from the MS 10, the HA 60 allows a corresponding IP address to be used when a method of statically assigning the IP address is employed. On the other hand, when a method of dynamically assigning the IP address is employed, the HA 60 allows an IP address to be used by assigning the IP address and transmitting a registration reply message. When the MS 10 moves to another PDSN area, it notifies the HA 60 of the PDSN area.
A Dynamic Host Configuration Protocol (DHCP) server/Domain Name System (DNS) server 70 is indicative of a server capable of automatically assigning users IP addresses. The DHCP server/DNS server 70 is used for establishing an IP address, a domain name, etc.
The DNS server is used for converting a host name into an IP address and vice versa. The DNS server may update an IP address for a specific host name upon receiving a DNS update message according to the RFC2136 protocol.
When the MS 10 capable of using a packet data service over the above-mentioned mobile communication network requests the packet data service, the BSC 23 and PCF 25 determine which PDSN should transmit packet data. At this time, a radio traffic channel and a radio link protocol (RLP) are established between the MS 10 and the BSC 23. The A8 interface is used to provide a path for user traffic between the BSC 23 and the PCF 25 for packet data services. In addition, the A10 interface is used to provide a path for user traffic between the PCF 25 and the PDSN 40 for packet data services. In this case, the packet data service in an ‘active’ state implies that the MS 10 occupies a radio traffic channel, maintains the RLP link and the A8 link, and transmits/receives packet data.
FIG. 2 is a schematic diagram showing a protocol stack for data call transfer in a conventional mobile communication system. The protocol stack includes a physical layer, a Radio Link Protocol (RLP), a Point-to-Point Protocol (PPP), an Internet Protocol (IP), a Transmission Control Protocol (TCP), a User Datagram Protocol (UDP), etc.
The physical layer is the lowest layer of the Open System Interconnection Reference Model (OSI Reference Model), an International Standards Organization (ISO) standard for worldwide communications that defines a framework for implementing protocols in seven layers. The physical layer, which is implemented in hardware, defines all electrical and physical specifications for devices. IS-953/2000 protocol 109 corresponds to the physical layer.
The RLP 107 is used to provide reliable data service over the air interface between the MS 10 and a base station. The RLP 107 also employs an Automatic Repeat Request (ARQ) scheme to request retransmission of messages which have errors or fail to arrive in order to ensure reliable transfer of data.
The PPP 105 is a method of connecting a computer to the Internet using a phone line. Working in the data link layer of the OSI Reference Model, the PPP 105 sends the computer's TCP/IP packets to a server that puts them onto the Internet.
The IP 103 is a data-oriented protocol used by source and destination hosts for communicating data across a packet-switched internetwork. The IP 103 specifies the format of packets, also called datagrams, and the addressing scheme.
The TCP is a connection-oriented, reliable delivery byte-stream transport layer protocol. Whereas the IP 103 protocol deals only with packets, the TCP enables two hosts to establish a connection and exchange streams of data. The TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.
The UDP is an alternative to the TCP and, together with IP, is sometimes referred to as UDP/IP. Like the TCP, the UDP uses the IP 103 to actually get packets from one computer to another. Unlike TCP, the UDP does not provide the service of dividing a message into packets (datagrams) and reassembling it at the other end. Specifically, the UDP does not provide sequencing of the packets that the data arrives in. This means that the application program that uses UDP must be able to make sure that the entire message has arrived and is in the right order. Network applications that want to save processing time because they have very small data units to exchange may prefer UDP to TCP.
The MS 10 establishes a session with a communication network connection unit such as the PCF 25 using the physical layer and the RLP. The MS 10 establishes a PPP session with the PDSN 40.
The MS 10 establishes a session with a supplementary service unit, which is provided in a mobile communication service system, using the TCP/IP or UDP/IP. Wireless data communications using the TCP/IP or UDP/IP is available only when a PPP connection is established between the MS and the PDSN.
Examples of applications required for accessing the Internet via the mobile communication terminal include a browser and a software platform such as JAVA, Binary Runtime Environment for Wireless (BREW), or Graphics Virtual Machine (GVM).
In the case when the MS or a communication server detects one or more errors during TCP communication in the above-mentioned communication network, a congestion control scheme widely used in typical wireline network communications has been used for error processing. Specifically, in the case when a communication error is detected from a received TCP packet or an acknowledgement (ACK) response to a transmitted packet is not received until a TCP's retransmission timer expires, the MS or the communication server determines the packet to have been lost due to congestion, and reduces the congestion window size of a transmission side to retransmit the packet.
The reduction in congestion window size leads to a significant decrease in the effective transfer rates of the transmission side. The occurrence of packet losses in a typical wireline network is mainly caused by a waiting time based on a priority logic mechanism in a routing process. However, in case of the radio network, the packet losses may occur due to a high bit error rate (BER) compared to that of the wireline network, or multi-path fading. In addition, the packet losses in the radio network may occur due to the rerouting of packets during handoff. Consequently, determining the packet losses in the radio network to have occurred due to congestion causes a problem in terms of transmission efficiency.